Detecting near-surface moisture stress in Sphagnum spp

• Published in: Remote sensing of environment Vol. 97; no. 3; pp. 371 - 381
• Main Authors: Harris, A., Bryant, R.G., Baird, A.J.
• Format: Journal Article
• Language: English
• Published: New York, NY Elsevier Inc 15-08-2005; Elsevier Science
• Subjects: Animal, plant and microbial ecology; Applied geophysics; Biological and medical sciences; Carbon balance; Earth sciences; Earth, ocean, space; Exact sciences and technology; Fundamental and applied biological sciences. Psychology; General aspects. Techniques; Internal geophysics; Moisture; Remote sensing; Spectral reflectance; Sphagnum; Teledetection and vegetation maps; Moisture; Spectral reflectance; Carbon balance; Remote sensing; Sphagnum; mass balance; vegetation; Water stress; bryophytes; Spectral data; Reflection spectrometry; Near infrared spectrometry; carbon; peat bogs; humidity; Water absorption; dehydration; Rewetting; Species; laboratory studies; Musci; detection; hydrology; reflectance; Plantae; chlorophyll; remote sensing; Biophysics; monitoring; Canopy(vegetation)
• ISSN: 0034-4257; 1879-0704
• DOI: 10.1016/j.rse.2005.05.001

Estimating near-surface moisture conditions from the reflectance spectra (400–2500 nm) of
Sphagnum moss offers great opportunities for the use of remote sensing as a tool for large-scale detailed monitoring of near-surface peatland hydrological conditions. This article investigates the effects of changes in near-surface and surface moisture upon the spectral characteristics of
Sphagnum moss. Laboratory-based canopy reflectance data were collected from two common species of
Sphagnum subjected to drying and subsequent rewetting. Several spectral indices developed from the near infra-red (NIR) and shortwave infra-red (SWIR) liquid water absorption bands and two biophysical indices (REIP and the chlorophyll index) were correlated with measures of near-surface moisture. All spectral indices tested were significantly correlated with near-surface moisture (with
r between 0.27 and 0.94). The strongest correlations were observed using indices developed from the NIR liquid water absorption features (fWBI
980 and fWBI
1200). However, a hysteretic response was observed in both NIR indices when the canopies were re-hydrated, a finding which may have implications for the timing of remote sensing image acquisition. The Moisture Stress Index (MSI), developed from the SWIR liquid water absorption feature also showed strong correlations with near-surface wetness although the range of moisture conditions over which the index was able to detect change was highly dependent on
Sphagnum species. Of the biophysical spectral indices tested (REIP and the chlorophyll index), the most significant relationships were observed between the chlorophyll index and near-surface wetness. All spectral indices tested were species specific, and this is attributed to differences in canopy morphology between
Sphagnum species. The potential for developing estimations of surface and near-surface hydrological conditions across northern peatlands using remote sensing technology is discussed.